Adaptive wireless energy transfer system

ABSTRACT

Exemplary embodiments are directed to wireless power transfer using magnetic resonance in a coupling mode region between a charging base (CB) and a remote system such as a battery electric vehicle (BEV). The wireless power transfer can occur from the CB to the remote system and from the remote system to the CB. Load adaptation and power control methods can be employed to adjust the amount of power transferred over the wireless power link, while maintaining transfer efficiency.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application is a continuation of U.S. patent application Ser. No.13/110,874, filed on May 18, 2011. U.S. patent application Ser. No.13/110,874 claims the benefit of U.S. Provisional Patent Application61/346,378 entitled “ADAPTIVE WIRELESS ENERGY TRANSFER SYSTEM” filed onMay 19, 2010, and claims the benefit of U.S. Provisional PatentApplication 61/367,802 entitled “ADAPTIVE WIRELESS ENERGY TRANSFERSYSTEM” filed on Jul. 26, 2010. Each of these applications is herebyexpressly incorporated by reference in its entirety.

BACKGROUND

1. Field

The present invention relates generally to wireless power transfer, andmore specifically to devices, systems, and methods related to wirelesspower transfer to remote systems such as vehicles including batteries.

2. Background

Approaches are being developed that use over-the-air or wireless powertransmission between a transmitter and a receiver coupled to theelectronic device to be charged. Such approaches generally fall into twocategories. One is based on the coupling of plane wave radiation (alsocalled far-field radiation) between a transmit antenna and a receiveantenna on the device to be charged. The receive antenna collects andrectifies the radiated power for charging the battery. This approachsuffers from the fact that the power coupling falls off quickly withdistance between the antennas, so charging over reasonable distances(e.g., less than 1 to 2 meters) becomes difficult. Additionally, sincethe transmitting system radiates plane waves, unintentional radiationcan interfere with other systems if not properly controlled throughfiltering.

Other approaches to wireless energy transmission techniques are based oninductive coupling between a transmit antenna embedded, for example, ina “charging” mat or surface and a receive antenna (plus a rectifyingcircuit) embedded in the electronic device to be charged. This approachhas the disadvantage that the spacing between transmit and receiveantennas must be very close (e.g., within millimeters). Though thisapproach does have the capability to simultaneously charge multipledevices in the same area, this area is typically very small and requiresthe user to accurately locate the devices to a specific area.

Recently, remote systems such as vehicles have been introduced thatinclude locomotion power from electricity and batteries to provide thatelectricity. Hybrid electric vehicles include on-board chargers that usepower from vehicle braking and traditional motors to charge thevehicles. Vehicles that are solely electric must receive the electricityfor charging the batteries from other sources. These electric vehiclesare conventionally proposed to be charged through some type of wiredalternating current (AC) such as household or commercial AC supplysources.

Efficiency is of importance in a wireless power transfer system due tothe losses occurring in the course of wireless transmission of power.Since wireless power transmission is often less efficient than wiredtransfer, efficiency is of an even greater concern in a wireless powertransfer environment. As a result, there is a need for methods andapparatuses that provide wireless power to electric vehicles.

A wireless charging system for electric vehicles may require transmitand receive antennas to be aligned within a certain degree. Differencesin distance and alignment of transmit and receive antennas impactsefficient transmission. Therefore, a need exists for adapting linkparameters in a wireless power transfer system in order to improve powertransfer, efficiency, and regulatory compliance.

SUMMARY

Exemplary embodiments are directed to wireless power transfer usingmagnetic resonance in a coupling mode region between a charging base(CB) and a remote system such as a battery electric vehicle (BEV). Thewireless power transfer can occur from the CB to the remote system andfrom the remote system to the CB. Load adaptation and power controlmethods can be employed to adjust the amount of power transferred overthe wireless power link, while maintaining transfer efficiency. In oneor more exemplary embodiments, an adaptable power converter isconfigurable between at least first and second modes to convert powerfrom and to a power supply system at an operating frequency in atransmit mode and vice versa in a receive mode. A charging base antennais configured for resonance near the operating frequency and operablycoupled to the adaptable power converter and configured to couplewireless energy with a remote antenna. The modes are selectable tosubstantially maintain an efficiency in the adaptable power converterover a varying coupling coefficient between the charging base antennaand the remote antenna. One or more exemplary embodiments also includemethods for performing the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless charging system for remote systems such asBEVs equipped with a wireless receiver while the BEV is parked near awireless transmitter.

FIG. 2 is a simplified block diagram of a wireless power charging systemfor a BEV.

FIG. 3 is a more detailed block diagram of a wireless power chargingsystem for a BEV illustrating communication links, guidance links, andalignment systems for the transmit antenna and receive antenna.

FIG. 4 illustrates a frequency spectrum showing various frequencies thatmay be available for wireless charging of BEVs.

FIG. 5 illustrates some possible frequencies and transmission distancesthat may be useful in wireless charging of BEVs.

FIG. 6 shows a simplified diagram of a replaceable contactless batterydisposed in a BEV.

FIG. 7 is a detailed diagram of a wireless power antenna and ferritematerial placement relative to a battery.

FIG. 8 is a simplified block diagram of portions of a battery system ina BEV equipped to wirelessly receive or transmit power.

FIG. 9 illustrates a parking lot comprising a plurality of parkingspaces and a charging base positioned within each parking space, inaccordance with an embodiment of the present invention.

FIG. 10A illustrates various obstructions that may be encountered by avehicle, which may require chassis clearance.

FIG. 10B illustrates a wireless power antenna located within a cavity ofthe underside of the chassis of a vehicle according to an exemplaryembodiment of the present invention.

FIG. 11 illustrates several variants of embedding a charging baseaccording to exemplary embodiments of the present invention.

FIGS. 12A-12C illustrate a vehicle including a wireless power antennapositioned over a charging base including a wireless power antennaaccording to an exemplary embodiment of the present invention.

FIGS. 13A and 13B illustrate possible locations in the X and Y directionthat a mechanical device may adjust the position of a wireless powerantenna according to an exemplary embodiment of the present invention.

FIG. 14 illustrates another mechanical solution in which the wirelesspower antenna may be repositioned by a gear shaft operably coupled to adrive mechanism according to an exemplary embodiment of the presentinvention.

FIG. 15 illustrates distance constraints for energy transfer, accordingto an exemplary embodiment of the present invention.

FIG. 16 is a circuit diagram for wireless power transfer system, inaccordance with an exemplary embodiment of the present invention.

FIG. 17 illustrates transmit and receive loop antennas showing magneticfield strength relative to radius of the antennas.

FIG. 18 illustrates an adaptable power conversion reconfigurable as afull-bridge power conversion and a half-bridge, in accordance with anexemplary embodiment of the present invention.

FIGS. 19A and 19B illustrate a half-bridge power conversionconfiguration and a Full-bridge power conversion configuration, inaccordance with an exemplary embodiment of the present invention.

FIG. 20 illustrates wireless power transfer components for a wirelesspower transfer system, in accordance with an exemplary embodiment of thepresent invention.

FIG. 21 illustrates various sensors for gathering measurements, inaccordance with an exemplary embodiment of the present invention.

FIG. 22 is a flowchart of a method for adaptive power conversion, inaccordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention can be practiced. The term “exemplary”used throughout this description means “serving as an example, instance,or illustration,” and should not necessarily be construed as preferredor advantageous over other exemplary embodiments. The detaileddescription includes specific details for the purpose of providing athorough understanding of the exemplary embodiments of the invention. Itwill be apparent to those skilled in the art that the exemplaryembodiments of the invention may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the novelty of theexemplary embodiments presented herein.

The term “wireless power” is used herein to mean any form of energyassociated with electric fields, magnetic fields, electromagneticfields, or otherwise that is transmitted from a transmitter to areceiver without the use of physical electromagnetic conductors.

Moreover, the term “wireless charging” is used herein to mean providingwireless power to one or more electrochemical cells or systems includingelectrochemical cells for the purpose of recharging the electrochemicalcells.

The term “battery electric vehicle” (BEV) is used herein to mean aremote system, and example of which is a vehicle that includes, as partof its locomotion abilities, electrical power derived from one or morerechargeable electrochemical cells. As non-limiting examples, some BEVsmay be hybrid electric vehicles that include on-board chargers that usepower from vehicle deceleration and traditional motors to charge thevehicles, other BEVs may draw all locomotion ability from electricalpower. Other “remote systems” are contemplated including electronicdevices and the like. Various terms and acronyms are used hereinincluding, but not limited to, the following:

-   AC Alternative Current-   BEV Battery Electric Vehicle-   CB Charging Base-   DC Direct Current-   EV Electric Vehicle-   FDX Full Duplex-   FET Field Effect Transistor-   G2V Grid-to-Vehicle-   HDX Half Duplex-   IGBT Insulated Gate Bipolar Transistor-   ISM Industrial Scientific and Medical-   LF Low Frequency-   PWM Pulse Width Modulation-   r.m.s. Root Mean Square-   VLF Very Low Frequency-   V2G Vehicle-to-Grid-   ZSC Zero Current Switching

By way of example and not limitation, a remote system is describedherein in the form of a Battery Electric Vehicle (BEV). Other examplesof remote systems are also contemplated including various electronicdevices and the like capable of receiving and transferring wirelesspower.

FIG. 1 illustrates a wireless charging system for wireless chargingenabled remote systems such as BEVs 102 while the BEV is parked near awireless charging base (CB) 103. Two vehicles 102 are illustrated in aparking area 106 and parked over corresponding CBs 104. A localdistribution center 108 is connected to a power backbone and isconfigured to provide an Alternating Current (AC) or a Direct Current(DC) supply to power conversion systems 112 as part of the CBs 104. TheCBs 104 also include wireless power antennas 114 for generating amagnetic near field or picking-up energy from a magnetic near-field by aremote antenna. Each vehicle includes batteries, a BEV power conversionand charging system 116 and a wireless power antenna 118 interactingwith the CB antenna 114 via the near-field.

In some exemplary embodiments the BEV antenna 118 may be aligned withthe CB antenna 114 and, therefore, disposed within the near-field regionsimply by the driver positioning the vehicle correctly relative to theCB antenna 114. In other exemplary embodiments, the driver may be givenvisual feedback, auditory feedback, or combinations thereof to determinewhen the vehicle is properly placed for wireless power transfer. In yetother exemplary embodiments, the vehicle may be positioned by anautopilot system, which may move the vehicle back and forth (e.g., inzig-zag movements) until an alignment error has reached a tolerablevalue. This may be performed automatically and autonomously by thevehicle without or with only minimal driver intervention provided thatthe vehicle is equipped with a servo steering wheel, ultrasonic sensorsall around and artificial intelligence. In still other exemplaryembodiments, the BEV antenna 118, the CB antenna 114, or a combinationthereof may include means for displacing and moving the antennasrelative to each other to more accurately orient them and develop a moredesireable near-field coupling therebetween.

The CBs 104 may be located in a variety of locations. As non-limitingexamples, some suitable locations are a parking area at a home of thevehicle owner, parking areas reserved for BEV wireless charging modeledafter conventional petroleum-based filling stations, and parking lots atother locations such as shopping centers and places of employment.

These BEV charging stations may provide numerous benefits, such as, forexample:

-   -   Convenience: charging can be performed automatically virtually        without driver intervention and manipulations.    -   Reliability: there may be no exposed electrical contacts and no        mechanical wear out.    -   Safety: manipulations with cables and connectors may not be        needed, and there may be no cables, plugs, or sockets that may        be exposed to moisture and water in an outdoor environment.    -   Vandalism resistant: There may be no sockets, cables, and plugs        visible nor accessible.    -   Availability: if BEVs will be used as distributed storage        devices to stabilize the grid. Availability can be increased        with a convenient docking-to-grid solution enabling Vehicle to        Grid (V2G) capability.    -   Esthetical and non-impedimental: There may be no column loads        and cables that may be impedimental for vehicles and/or        pedestrians.

As a further explanation of the V2G capability, the wireless powertransmit and receive capabilities can be configured as reciprocal suchthat the CB 104 transfers power to the BEV 102 and the BEV transferspower to the CB 104. This capability may be useful for powerdistribution stability by allowing BEVs to contribute power to theoverall distribution system in a similar fashion to how solar-cell powersystems may be connected to the power grid and supply excess power tothe power grid.

FIG. 2 is a simplified block diagram of a wireless power charging system130 for a BEV. Exemplary embodiments described herein use capacitivelyloaded wire loops (i.e., multi-turn coils) forming a resonant structurethat is capable to efficiently couple energy from a primary structure(transmitter) to a secondary structure (receiver) via the magnetic nearfield if both primary and secondary are tuned to a common resonancefrequency. The method is also known as “magnetic coupled resonance” and“resonant induction.”

To enable wireless high power transfer, some exemplary embodiments mayuse a frequency in the range from 20-60 kHz. This low frequency couplingmay allow highly efficient power conversion that can be achieved usingstate-of-the-art solid state devices. In addition, there may be lesscoexistence issues with radio systems compared to other bands.

In FIG. 2, a conventional power supply 132, which may be AC or DC,supplies power to the CB power conversion module 134, assuming energytransfer towards vehicle. The CB power conversion module 134 drives theCB antenna 136 to emit a desired frequency signal. If the CB antenna 136and BEV antenna 138 are tuned to substantially the same frequencies andare close enough to be within the near-field radiation from the transmitantenna, the CB antenna 136 and BEV antenna 138 couple such that powermay be transferred to the BEV antenna 138 and extracted in the BEV powerconversion module 140. The BEV power conversion module 140 may thencharge the BEV batteries 142. The power supply 132, CB power conversionmodule 134, and CB antenna 136 make up the infrastructure part 144 of anoverall wireless power system 130, which may be stationary and locatedat a variety of locations as discussed above. The BEV battery 142, BEVpower conversion module 140, and BEV antenna 138 make up a wirelesspower subsystem 146 that is part of the vehicle or part of the batterypack.

In operation, assuming energy transfer towards the vehicle or battery,input power is provided from the power supply 132 such that the CBantenna 136 generates a radiated field for providing the energytransfer. The BEV antenna 138 couples to the radiated field andgenerates output power for storing or consumption by the vehicle. Inexemplary embodiments, the CB antenna 136 and BEV antenna 138 areconfigured according to a mutual resonant relationship and when theresonant frequency of the BEV antenna 138 and the resonant frequency ofthe CB antenna 136 are very close, transmission losses between the CBand BEV wireless power subsystems are minimal when the BEV antenna 138is located in the near-field of the CB antenna 136.

As stated, an efficient energy transfer occurs by coupling a largeportion of the energy in the near-field of a transmitting antenna to areceiving antenna rather than propagating most of the energy in anelectromagnetic wave to the far-field. When in this near-field acoupling mode may be developed between the transmit antenna and thereceive antenna. The area around the antennas where this near-fieldcoupling may occur is referred to herein as a near field coupling-moderegion.

The CB and the BEV power conversion module may both include anoscillator, a power amplifier, a filter, and a matching circuit forefficient coupling with the wireless power antenna. The oscillator isconfigured to generate a desired frequency, which may be adjusted inresponse to an adjustment signal. The oscillator signal may be amplifiedby the power amplifier with an amplification amount responsive tocontrol signals. The filter and matching circuit may be included tofilter out harmonics or other unwanted frequencies and match theimpedance of the power conversion module to the wireless power antenna.The CB and BEV power conversion module may also include, a rectifier,and switching circuitry to generate a suitable power output to chargethe battery.

BEV and CB antennas used in exemplary embodiments may be configured as“loop” antennas, and more specifically, multi-turn loop antennas, whichmay also be referred to herein as a “magnetic” antenna. Loop (e.g.,multi-turn loop) antennas may be configured to include an air core or aphysical core such as a ferrite core. An air core loop antenna may allowthe placement of other components within the core area. Physical coreantennas including ferromagnetic or ferromagnetic materials may allowdevelopment of a stronger electromagnetic field and improved coupling.

As stated, efficient transfer of energy between a transmitter andreceiver occurs during matched or nearly matched resonance between atransmitter and a receiver. However, even when resonance between atransmitter and receiver are not matched, energy may be transferred at alower efficiency. Transfer of energy occurs by coupling energy from thenear-field of the transmitting antenna to the receiving antenna residingin the neighborhood where this near-field is established rather thanpropagating the energy from the transmitting antenna into free space.

The resonant frequency of the loop antennas is based on the inductanceand capacitance. Inductance in a loop antenna is generally simply theinductance created by the loop, whereas, capacitance is generally addedto the loop antenna's inductance to create a resonant structure at adesired resonant frequency. As a non-limiting example, a capacitor maybe added in series with the antenna to create a resonant circuit thatgenerates a magnetic field. Accordingly, for larger diameter loopantennas, the size of capacitance needed to induce resonance decreasesas the diameter or inductance of the loop increases. It is further notedthat inductance may also depend on a number of turns of a loop antenna.Furthermore, as the diameter of the loop antenna increases, theefficient energy transfer area of the near-field increases. Of course,other resonant circuits are possible. As another non-limiting example, acapacitor may be placed in parallel between the two terminals of theloop antenna (i.e., parallel resonant circuit).

Exemplary embodiments of the invention include coupling power betweentwo antennas that are in the near-fields of each other. As stated, thenear-field is an area around the antenna in which electromagnetic fieldsexist but may not propagate or radiate away from the antenna. Near-fieldcoupling-mode regions are typically confined to a volume that is nearthe physical volume of the antenna e.g. within a radius of one sixth ofthe wavelength. In the exemplary embodiments of the invention, magnetictype antennas such as single and multi-turn loop antennas are used forboth transmitting and receiving since magnetic near-field amplitudes inpractical embodiments tend to be higher for magnetic type antennas incomparison to the electric near-fields of an electric-type antenna(e.g., a small dipole). This allows for potentially higher couplingbetween the pair. Another reason for relying on a substantially magneticfield is its low interaction with non-conductive dielectric materials inthe environment and the safety issue. Electric antennas for wirelesshigh power transmission may involve extremely high voltages.Furthermore, “electric” antennas (e.g., dipoles and monopoles) or acombination of magnetic and electric antennas is also contemplated.

FIG. 3 is a more detailed block diagram of a generic wireless powercharging system 150 for a BEV illustrating communication links 152,guidance links 154, and alignment systems 156 for the CB antenna 158 andBEV antenna 160. As with the exemplary embodiment of FIG. 2 and assumingenergy flow towards BEV, in FIG. 3 the CB power conversion unit 162receives AC or DC power from the CB power interface 164 and excites theCB antenna 158 at or near its resonant frequency. The BEV antenna 160,when in the near field coupling-mode region, receives energy from thenear field coupling mode region to oscillate at or near the resonantfrequency. The BEV power conversion unit 166 converts the oscillatingsignal from the receive antenna 160 to a power signal suitable forcharging the battery.

The generic system may also include a CB communication unit 168 and aBEV communication unit 170, respectively. The CB communication unit 168may include a communication interface to other systems (not shown) suchas, for example, a computer, and a power distribution center. The BEVcommunication unit 170 may include a communication interface to othersystems (not shown) such as, for example, an on-board computer on thevehicle, other battery charging controller, other electronic systemswithin the vehicles, and remote electronic systems.

The CB and BEV communication units may include subsystems or functionsfor specific application with separate communication channels therefore.These communications channels may be separate physical channels or justseparate logical channels. As non-limiting examples, a CB alignment unit172 may communicate with a BEV alignment unit 174 to provide a feedbackmechanism for more closely aligning the CB antenna 158 and BEV antenna160, either autonomously or with operator assistance. Similarly, a CBguide unit 176 may communicate with a BEV guide unit 178 to provide afeedback mechanism to guide an operator in aligning the CB antenna 158and BEV antenna 160. In addition, there may be a separategeneral-purpose communication channel 152 supported by CB communicationunit 180 and BEV communication unit 182 for communicating otherinformation between the CB and the BEV. This information may includeinformation about EV characteristics, battery characteristics, chargingstatus, and power capabilities of both the CB and the BEV, as well asmaintenance and diagnostic data. These communication channels may beseparate physical communication channels such as, for example,Bluetooth, zigbee, cellular, etc.

In addition, some communication may be performed via the wireless powerlink without using specific communications antennas. In other words thecommunications antenna and the wireless power antenna are the same.Thus, some exemplary embodiments of the CB may include a controller (notshown) for enabling keying type protocol on the wireless power path. Bykeying the transmit power level (Amplitude Shift Keying) at predefinedintervals with a predefined protocol, the receiver can detect a serialcommunication from the transmitter. The CB power conversions module 162may include a load sensing circuit (not shown) for detecting thepresence or absence of active BEV receivers in the vicinity of thenear-field generated by the CB antenna 158. By way of example, a loadsensing circuit monitors the current flowing to the power amplifier,which is affected by the presence or absence of active receivers in thevicinity of the near-field generated by CB antenna 158. Detection ofchanges to the loading on the power amplifier may be monitored by thecontroller for use in determining whether to enable the oscillator fortransmitting energy, to communicate with an active receiver, or acombination thereof.

BEV circuitry may include switching circuitry (not shown) for connectingand disconnecting the BEV antenna 160 to the BEV power conversion unit166. Disconnecting the BEV antenna not only suspends charging, but alsochanges the “load” as “seen” by the CB transmitter, which can be used to“cloak” the BEV receiver from the transmitter. The load changes can bedetected if the CB transmitter includes the load sensing circuit.Accordingly, the CB has a mechanism for determining when BEV receiversare present in the CB antenna's near-field.

FIG. 4 illustrates a frequency spectrum showing various frequencies thatmay be available and suitable for wireless charging of BEVs. Somepotential frequency ranges for wireless high power transfer to BEVsinclude: VLF in a 3 kHz to 30 kHz band, lower LF in a 30 kHz to 150 kHzband (for ISM-like applications) with some exclusions, HF 6.78 MHz(ITU-R ISM-Band 6.765-6.795 MHz), HF 13.56 MHz (ITU-R ISM-Band13.553-13.567), and HF 27.12 MHz (ITU-R ISM-Band 26.957-27.283).

FIG. 5 illustrates some possible frequencies and transmission distancesthat may be useful in wireless charging of BEVs. Some exampletransmission distances that may be useful for BEV wireless charging areabout 30 mm, about 75 mm, and about 150 mm. Some exemplary frequenciesmay be about 27 kHz in the VLF band and about 135 kHz in the LF band.

Many considerations should be taken into account on determining asuitable frequency beyond just the resonance characteristics andcoupling-mode region of the receive and transmit antennas. Wirelesspower frequencies may interfere with frequencies used for otherapplications. As non-limiting examples, there may be VLF/LF coexistenceissues with power line frequencies, audible frequencies andcommunication frequencies. Some non-limiting examples where coexistencemay be an issue for VLF and LF are: frequencies for radio controlledclocks, frequencies for LW AM broadcasts and other radio services,cross-coupling to ISDN/ADSL and ISDN/xDSL communication channels,electronic vehicle immobilization systems, RFID (Radio FrequencyIdentification) systems, EAS (Electronic Article Surveillance) systems,on-site paging, Low Voltage PLC systems, medical implants (cardiacpacemakers, etc.), audio systems and acoustic emission perceivable byhumans and animals.

Some non-limiting examples where coexistence may be an issue for HFfrequencies are industrial, scientific and medical (ISM) radio bands,such as: 6.78 MHz for remote control applications and RFID in FDX or HDXmode with continuous energy transfer; 13.56 MHz for RFID in FDX or HDXmode with continuous energy transfer as well as portable device wirelesspower; and 27.12 MHz for Railway applications (Eurobalise 27.095 MHz),Citizen band radio, and remote control (e.g., models, toys, garage door,computer mouse, etc.).

FIG. 6 shows a simplified diagram of a rechargeable and/or replaceablebattery disposed in a battery electric vehicle (BEV) 220. In thisexemplary embodiment, the low battery position may be useful for abattery unit 222 that integrates a wireless power interface 226 and thatcan receive power from a charger embedded in the ground. In FIG. 6, theEV rechargeable battery unit 222 is accommodated in a batterycompartment 224. The battery unit 222 also provides a wireless powerinterface 226, which may integrate the entire BEV sided wireless powersubsystem comprising the resonant magnetic antenna, power conversion andother control and communications functions as needed for efficient andsafe wireless energy transfer between a ground-embedded charging base(CB) and the Electric Vehicle (EV) battery.

It may be useful for the BEV antenna to be integrated flush with abottom side of battery unit 222 (vehicle body) so that there are noprotrusive parts and so that the specified ground-to-vehicle bodyclearance can be maintained. This configuration may require some room inthe battery unit dedicated to the wireless power subsystem.

In some exemplary embodiments, the CB antenna and the BEV antenna arefixed in position and the antennas are brought within a near-fieldcoupling region by overall placement of the BEV relative to the CB.However, in order to perform energy transfer rapidly, efficiently, andsafely, the distance between the charging base antenna and the BEVantenna may need to be reduced to improve magnetic coupling. Thus, insome exemplary embodiments, the CB antenna and the BEV antenna may bedeployable moveable to bring them into better alignment. Alsoillustrated in FIG. 6 is a battery unit 222 that provides contactlesspower and communications interfaces 226/228.

FIG. 7 is a more detailed diagram of a loop antenna and ferrite materialplacement relative to a battery. In various exemplary embodiments, thebattery unit includes one of a deployable and non-deployable BEV antennamodule 240 as part of the wireless power interface. To prevent magneticfields from penetrating into the battery unit 230 and into the interiorof the vehicle, there may be a conductive shielding 232 (e.g., a coppersheet) between the battery unit and the vehicle. Furthermore, anon-conductive (e.g., plastic) layer 234 may be used to protect theconductive shield 232, the coil 236, and the ferrite material 238 fromall sorts of environmental impacts (e.g., mechanical damage,oxidization, etc.).

FIG. 7 shows a fully ferrite embedded antenna coil 236. The coil 236itself may be made, for example only, of stranded Litz wire. FIG. 7 alsoshows a dimensioned ferrite plate 238 (i.e., ferrite backing) to enhancecoupling and to reduce eddy currents (heat dissipation) in theconductive shield 232. The coil 236 may be fully embedded in anon-conducting non-magnetic (e.g. plastic) material 234. There may be aseparation between coil 236 and ferrite plate 238 in general, as theresult of a trade-off between magnetic coupling and ferrite hysteresislosses.

Furthermore, the coil 236 may be movable in lateral X and/or Ydirections. FIG. 7 specifically illustrates an exemplary embodimentwherein the antenna (coil) module 240 is deployed in a downward Zdirection. The physical separation of the antenna module 240 from thebattery unit 230 may have a positive effect on the antennas performance.

FIG. 8 is a simplified block diagram of portions of a battery system 250in a BEV equipped to receive wireless power. This exemplary embodimentillustrates wireless power interfaces that may be used between an EVsystem 252, a battery subsystem 254, and the wireless charging interfaceto a CB (not shown). The battery subsystem 254 provides for both energytransfer and communications with a wireless interface between the EV andthe battery subsystem 254, which enables a completely contactless,closed, and sealed battery subsystem. The interface may include thefunctionality for bidirectional (two-way) wireless energy transfer,power conversion, control, battery management, and communications. Whilea contactless connection between the battery and the BEV is illustrated,a contact connection is also contemplated.

The charger to battery communication interface 256 and wireless powerinterface 258 has been explained above and it shall be noted again thatFIG. 8 shows a generic concept. In specific embodiments, the wirelesspower antenna 260 and the communications antenna may be combined to asingle antenna. This may also apply to the battery-to-EV wirelessinterface 262. The power conversion (LF/DC) unit 264 converts wirelesspower received from the CB to a DC signal to charge the EV battery 266.A power conversion (DC/LF) 268 supplies power from the EV battery 266 toa wireless power interface 270 between the battery subsystem 254 and theEV system 252. A battery management unit 272 may be included to manageEV battery charging, control of the power conversion units (LF/DC andDC/LF), as well as a wireless communication interface.

In the EV system 252, a wireless power antenna 274 receives power fromantenna 276 and a LF/DC power conversion unit 278 may supply a DC signalto a super capacitor buffer 280. In some exemplary embodiments, LF/DCpower conversion unit 278 may supply a DC signal directly to the EVpower supply interface 282. In other exemplary embodiments, acontactless interface may not be capable of providing the high batterypeak current required by the vehicles drive train e.g., duringacceleration. To decrease the source resistance and thus the peak powercapability of the EVs energy storage system as “seen” at the EV powersupply terminals, an additional super capacitor buffer may be employed.An EV electrical system control unit 284 may be included to managecontrol of the power conversion unit (LF/DC) 278, charging of the supercapacitor buffer 280, as well as a wireless communication interface 262to the EV and the battery subsystem 254. Furthermore, it is noted thatV2G capabilities, as described above, may apply to the conceptsdescribed with reference to, and illustrated in, FIG. 8.

Exemplary embodiments of the present invention, as described below, aredirected toward alignment of wireless power antennas as part of awireless charging system for BEVs (also referred to herein as a “BEVwireless charging system”). As will be appreciated by a person havingordinary skill in the art, adequate antenna alignment may enable two-way(bidirectional) energy transfer between a charging base, positionedwithin, for example, a parking space, and a BEV subsystem, in a quick,efficient, and safe manner. According to one or more exemplaryembodiments, a vehicle guidance system may provide coarse alignment foradequately positioning a BEV within a parking space to enable a CBantenna and a BEV antenna to be aligned within a specific error radius.Furthermore, according to one or more other exemplary embodiments, anantenna alignment system may be configured to mechanically adjust aposition of a CB antenna, a BEV antenna, or both in one or moredirections to enable for fine alignment of antennas within a BEVwireless charging system.

FIG. 9 illustrates a parking lot 901 comprising a plurality of parkingspaces 907. It is noted that a “parking space” may also be referred toherein as a “parking area.” To enhance the efficiency of a vehiclewireless charging system, a BEV 905 may be aligned along an X direction(depicted by arrow 902 in FIG. 9) and a Y direction (depicted by arrow903 in FIG. 9) to enable a wireless power vehicle base 904 within BEV905 to be adequately aligned with a wireless power charging base 906within an associated parking space 907. Although parking spaces 907 inFIG. 9 are illustrated as having a single charging base 906, embodimentsof the present invention are not so limited. Rather, parking spaces arecontemplated that may have one or more charging bases.

Furthermore, embodiments of the present invention are applicable toparking lots having one or more parking spaces, wherein at least oneparking space within a parking lot may comprise a charging base.Furthermore, guidance systems (not shown) may be used to assist avehicle operator in positioning a BEV in a parking space 907 to enable avehicle base (e.g., vehicle base 904) within the BEV to be aligned witha charging base 906. Exemplary guidance systems may includeelectronic-based approaches (e.g., radio positioning, direction findingprinciples, and/or optical, quasi-optical and/or ultrasonic sensingmethods) or mechanical-based approaches (e.g., vehicle wheel guides,tracks or stops), or any combination thereof, for assisting a BEVoperator in positioning a BEV to enable an antenna within the BEV to beadequately aligned with a charging antenna within a charging base (e.g.,charging base 906).

FIG. 10A illustrates that various obstructions 1005 may be encounteredby a BEV 1010 requiring a minimum chassis clearance. The obstructions1005 may contact the underside 1015 of the chassis of the BEV 1010 atdifferent locations. When a wireless power antenna (not shown) islocated within or near the underside 1015 of the chassis of the BEV1010, the wireless power antenna may become damaged, misaligned, or haveother problems associated with obstructions 1005 contacting the wirelesspower antenna.

FIG. 10B illustrates a BEV antenna 1020 according to an exemplaryembodiment of the present invention. In order to protect the BEV antenna1020 from undesirable contact from obstructions, it may be desirable tolocate the BEV antenna 1020 within a cavity 1012 of the underside of thechassis of a BEV 1010.

A charging base may include a power conversion unit operably coupledwith a CB antenna. The charging base may further include othermechanical or electronic components (e.g., processor) that may be usedfor position adjustment of the CB antenna as will be described herein.Components of the charging base may be housed within a charging basethat is at least partially embedded below a ground surface, such as in aparking lot, driveway, or garage.

FIG. 11 illustrates a charging base 1110 at least partially embeddedbelow a ground surface 1105 according to an exemplary embodiment of thepresent invention. The charging base 1110 may include one or more CBantennas 1115 for transmitting or receiving a wireless power signalto/from a corresponding BEV antenna (not shown) associated with a BEV.The charging base 1110 may be protrusive 1101 from the ground, which mayimprove coupling as the distance between the CB antenna 1115 and BEVantenna may be reduced. A protrusive 1101 charging base 1110 may be moreaccessible for maintenance and repair. However, a protrusive 1101charging base 1110 may be an impediment, such as for pedestrians orduring snow removal.

Alternatively, the charging base 1110 may be flush 1102 with the surfaceof the ground 1105. A flush 1102 charging base 1110 may be moreaccessible for maintenance and repair and non-impedimental; however,coupling between the CB antenna 1115 and BEV antenna may be reduced incomparison to the protrusive 1101 charging base 1110. A flush 1102charging base 1110 may also leave a potential problem with the edge ofthe ground surface (e.g., asphalt) potentially being more prone toerosion by water, ice and mechanical stress.

Alternatively, a charging base 1110 may be located completely below 1103the surface of the ground (e.g., below the asphalt layer 1107). Such abelow-surface 1103 charging base 1110 may be more secure from intruders(e.g., vandalism), and be non-impedimental; however, coupling andaccessibility to maintenance and repair may be reduced.

FIG. 12A-12C illustrate a BEV 1210 including a wireless power antenna1215 positioned over a charging base 1220 also including a wirelesspower antenna 1225. As shown in FIGS. 12A-12C, the BEV antenna 1210 andthe CB antenna 1225 are aligned in the X and Y directions, and separatedby a distance 1230 in the Z direction. As shown in FIG. 12B, the BEVantenna 1210 and the CB antenna 1225 are misaligned by an offsetdistance 1235 in the X direction, and are separated by a distance 1230in the Z direction.

It may be desirable to reduce the distance 1230 and the offset distance1235 in order to improve coupling strength between the BEV antenna 1215and the CB antenna 1225. Reducing the distance 1230 and the offsetdistance 1235 may occur through a fine alignment adjustment system.

The fine alignment adjustment system may be used to adjust the physicalposition of the CB antenna 1225, the BEV antenna 1215, or a combinationthereof in order to increase coupling strength between the CB antenna1225 and the BEV antenna 1215. Adjusting the position of one or both ofthe BEV antenna 1215 and CB antenna 1225 may be performed in response toa detection of misalignment therebetween. Determining misalignment maybe performed by utilizing information from the vehicle guidance system,as described above, such as for the methods related to magnetic fielddetection. Furthermore, information from a wireless power link (e.g.,various parameters indicative of the performance of the wireless powerlink) may be used in determining misalignment of associated antennas.For example, during misalignment detection, the wireless power link maybe operated at a reduced power level and after associated antennas havebeen accurately aligned, the power level may be increased.

The fine alignment adjustment system may be separated from, or inaddition to the course alignment guidance system. For example, thecourse alignment guidance system may guide a BEV into a position withina given tolerance (i.e., error radius), such that a fine alignmentadjustment system can correct for fine errors between the BEV antenna1215 and the CB antenna 1225.

As shown in the overhead view of BEV 1210 in FIG. 12C, the BEV antenna1210 and the CB antenna 1225 are misaligned only in the X direction. TheBEV antenna 1210 and CB antenna 1220 are aligned in the Y direction. Forexample, the alignment in the Y direction may have been accomplished bythe BEV 1210 using its own traction system, which may be assisted (e.g.,auto-piloted) by the guidance system described herein, and by which theBEV's motor may be able to move smoothly and accurately to a target Yposition. In such a scenario, alignment error in the X direction maystill exist but not in the Y direction. Eliminating the need foralignment adjustment in the Y direction (e.g., through use of a coursealignment guidance system) may also reduce space requirements for BEVantenna 1215 as the BEV antenna 1215 may be configured to move only in Xdirection, which may be accommodated in a cavity and not deployed forwireless power transfer. Thus, eliminating the need for fine alignmentin the Y direction may simplify the BEV wireless power subsystem.

FIGS. 13A and 13B illustrate possible locations in the X and Y directionthat a mechanical device may adjust the position of a BEV antenna 1415according to an exemplary embodiment of the present invention. Forexample, by selecting an angle pair (α, β) within the mechanical device,any position in the X and Y directions may be achieved within a radiusr_(max).

FIG. 13B illustrates a mechanical solution for a BEV antenna 1515 thatis located within a cavity 1512 of the underside of a BEV 1510 accordingto an exemplary embodiment of the present invention. As shown in FIG.13B, mechanical device 1550 may adjust the position of the BEV antenna1515 in the X and Y directions by selecting an appropriate angle pair(α, β). Additionally, mechanical device 1550 may adjust the position ofthe BEV antenna 1515 in the Z direction by lowering the BEV antenna 1515from the cavity 1512 of the BEV 1510. Mechanical device 1550 may includeone of many mechanical solutions including electric driven mechanicsand/or hydraulics. Although not shown herein, a mechanical device maysimilarly be used to adjust the position of the CB antenna in the X, Y,or Z directions, or any combination thereof. In other words, finealignment adjustment may be accomplished with a mechanical solution foradjusting the position of the CB antenna, the BEV antenna 1515, or both,as the case may be.

FIG. 14 illustrates another mechanical solution in which the BEV antenna1615 (and/or CB antenna) may be repositioned by a gear shaft 1650operably coupled to a drive mechanism 1652 according to an exemplaryembodiment of the present invention. In operation, if the drivemechanism 1652 is actuated, the gear shaft 1650 may be rotated to extendthe support member 1654 in order to lower the BEV antenna 1615 in the Zdirection.

The fine alignment adjustment may also accomplished with the assistanceof an electrical solution (e.g., electronically switched coil arrays)altering the flux lines of the electric field generated by the wirelesspower transmitter. A combination of mechanical and electrical alignmentof the antennas may be used.

The BEV antenna may be located along the underside of the chassis ofBEV. Rather than the charging base being at least partially embeddedbelow the surface of the ground as previously described, a charging basemay be configured as a charging platform located above the surface ofthe ground. Such a configuration may be desirable as a retrofit solutionfor a garage or carport if forming a hole in the ground for a chargingbase is undesired. A configuration of a charging platform may alsoprovide flexibility as the charging platform may mobile and able to bestored in a location other than a garage or transferred to anotherlocation.

The charging base (e.g., charging platform) may be configured to moveautomatically (e.g., as an automated robot), be controlled remotely(e.g., via a remote control unit), or through other methods for controlof a mobile charging platform. For example, the BEV (e.g., through itswireless power subsystem) may request a charge, whereupon the chargingbase may move automatically underneath the BEV and position itself toalign the CB wireless power antenna with the BEV antenna. Further finealignment (if necessary) may be accomplished through adjusting theposition of the BEV antenna and CB antenna in one or more direction aspreviously described.

Once sufficiently aligned, charging base may more efficiently transferwireless power between a charging base and a wireless power subsystem ofthe BEV. After charging is completed, or after some other event, thecharging base may return back to a waiting position (standby mode). Thewireless power system may, therefore, include a communication link withthe charging base and another device (e.g., wireless power subsystem)associated with the BEV. The charging base may further include cablemanagement in order to uncoil and coil a connecting cable prior to andafter the charging process.

A wireless power charging system for a BEV may be further configured forsafety and security concerns. For example, the BEV may be configured tobe immobilized when the wireless power BEV or CB antennas are deployed,when such antennas cannot be retracted (e.g., due to damage orobstacle). Such immobilization may protect the wireless power chargingsystem from further damage. The wireless power charging system mayfurther include sensors that detect mechanical resistance of thewireless power BEV or CB antennas. Detecting mechanical resistance mayprotect the wireless power BEV or CB antennas and accompanyingcomponents from being damaged if an obstacle (stone, debris, snow,animal, etc.) is positioned in a location that would restrict themovement of the antenna.

The wireless power charging system may further include continuousmonitoring of the wireless power link between the BEV antenna and CBantenna (e.g., monitoring voltages, currents, power flow, etc.) andreduce the power transmitted or shut down power in the event ofdetection of an abnormality in the wireless power link. The wirelesspower charging system may further include sensors configured to detectthe presence of persons or animals in close proximity of the antenna.Such sensors may be desirable in order for a processor to reduce orterminate wireless power transmission if a person is proximate thewireless power antennas. Such an action may be a safety precautionagainst prolonged exposure to electromagnetic radiation, such as forexample, while a person performs maintenance or other repair workunderneath the BEV particularly for persons using cardiac pacemakers orsimilar sensitive and safety critical medical devices.

Wireless energy transmission principles are further described herein. Asdescribed above, wireless energy transfer uses capacitively loaded wireloops (or multi-turn coils) forming a resonant structure that canprovide strong coupling, thus capable of efficient energy transfer froma primary structure (e.g., transmitter) to a secondary structure (e.g.,receiver) via the magnetic near field if both primary and secondary aretuned to a common resonance frequency. Also as stated, the method mayalso be known as “magnetic coupled resonance” or “resonant induction.”

To enable wireless high power transfer, a frequency in the range from20-60 kHz is considered desirable because highly efficient powerconversion can be achieved using state-of-the-art solid state devicesand there may be less coexistence issues with radio systems compared toother bands. For calculations of power transfer, a BEV-mounted antennacoil that may be disk-shaped (as described above) and that can be movedhorizontally (generally in x,y direction) for alignment purposes as wellas vertically (z direction) is assumed. As described herein, the BEVantenna module may normally be stowed in vehicles underbody to benon-protrusive. When BEV is parked for charging, the antenna coil islifted down in the z direction to minimize the distance to the CBantenna coil that may also be disk-shaped (as described above) as wellas ground embedded.

FIG. 15 illustrates distance constraints for energy transfer, accordingto exemplary embodiments of the present invention. Minimum distance denables energy transfer at maximum efficiency and maximum power underregulatory constraints. Zero distance (antennas touching) would beoptimum. However in a practical solution that needs to be robust,flexible and reliable, a certain separation is expected. Thisirreducible distance will depend on several thickness factors such as(1) environmental (presence of dirt, debris, snow, mainly in an outdoorparking) illustrated as debris thickness 1680, (2) embedding of CBantenna coil in ground (below asphalt, flush, protrusive) illustrated asasphalt thickness 1682, (3) housing of CB and BEV antenna moduleillustrated as coil thickness 1684, cover thickness 1686 for the CB andcoil thickness 1688 and cover thickness 1690 for the BEV, (4) safetymargin thickness 1692 required to absorb sudden vertical displacements(shocks) of vehicles suspension system (e.g. if a heavy person sits downin a car while BEV antenna is deployed), etc., as illustrated in FIG.15.

Ideally, the system adapts to the actual conditions with an objective tominimize the distance and thus maximizing the performance of thewireless power transfer. In such an exemplary adaptive system,separation of the CB and the BEV antenna coil may be variable requiringcertain link parameters to be adapted accordingly if maximum power,maximum efficiency and regulatory compliance is to be addressed. Thisadaptation is further described herein below.

FIG. 16 illustrates a circuit diagram containing elements of a wirelesspower system, in accordance with an exemplary embodiment, based on aseries resonant inductive link. Both a power source and a power sink(load) are assumed constant voltage with voltages V_(SDC) and V_(LDC)respectively, reflecting the characteristics of the power grid and theBEV battery, respectively. Constant voltage shall be understood in thesense of a virtually zero source resistance and zero sink resistance,respectively.

The circuit diagram of FIG. 16 as well as the following descriptionassumes energy transfer from a CB-side source 1702 to a BEV-side sink1704. However, this should not exclude energy transfer in reversedirection, for example, for purposes of vehicle-to-grid (V2G) energytransfer, provided that power conversion supports reverse power flow(bidirectional, four quadrant control).

FIG. 17 illustrates a CB antenna coil 1706 and a BEV antenna coil 1708that are separated by distance d and are represented in FIG. 16 by theirinductances L₁ and L₂, respectively and their mutual couplingcoefficient k(d) that is a function of distance. Capacitors C₁ and C₂are used to compensate for antenna inductance, thus to achieve resonanceat desired frequency. Equivalent resistances R_(eq,1) and R_(eq,2)represent the losses inherent to the antenna coils and theanti-reactance capacitors.

FIG. 17 illustrates CB and BEV antenna coils that are separated bydistance d and are represented in FIG. 16 by their inductances L₁ andL₂, respectively and their mutual coupling coefficient k(d) that is afunction of distance. Capacitors C₁ and C₂ are used to compensate forantenna inductance, thus to achieve resonance at desired frequency.Equivalent resistances R_(eq,1) and R_(eq,2) represent the lossesinherent to the antenna coils and the anti-reactance capacitors. FIG. 17also indicates the magnetic field vector H(r) that is generated by thepair of coils at a position r in the vicinity of the wireless powersystem.

In the exemplary embodiment illustrated in FIG. 16, CB-side powerconversion converts DC power into AC power at a desired frequency(operating frequency), preferably in the VLF or LF range, for example,from 20 kHz to 60 kHz for the high power application of concern. In thefollowing, any frequency in this range is generally called LF.

In another embodiment however, CB-side power conversion may also convertAC power at a standard mains frequency into AC power at an operatingfrequency suitable for wireless power. In yet another exemplaryembodiment, CB-side power conversion may convert unfiltered DC (e.g.AC-pulsed DC power) into AC power at an operating frequency. In thesetwo latter embodiments, power generated at operating frequency may benon-constant envelope.

A transformation ratio 1:n₁ can also be attributed to CB powerconversion. and may be defined as

1:n ₁ =V _(SDC) :V ₁  Equation 1

where V_(SDC) and V₁ denote the DC input voltage and the r.m.s. voltageof the fundamental frequency at LF output, respectively.

BEV-side power conversion performs reverse operation reconverting LFpower received by BEV antenna back to DC power. Correspondingly, atransformation ratio n₂:1 is attributed to CB power conversion, whichmay be defined as

n ₂:1=V ₂ :V _(LDC)  Equation 2

where V₂ and V_(LDC) denote the r.m.s. voltage of the fundamentalfrequency at LF input and the DC output voltage, respectively.

Theory shows that efficiency and power of an inductively coupledresonant link reach a maximum, if resonance of both CB and BEV antennaare adjusted to the operating frequency. This is valid for any couplingcoefficient 0<k(d)<1. In practice, power conversion may require thesystem to be operated slightly off resonance, if zero current switchingis targeted. This can be explained by phase offset of harmonicscomponents contained in the antenna current. For example, the system maybe operated within a first range of the resonance frequency. The firstrange may be, for example, a range within about +/−10 kHz, about +/−5kHz, or about +/−1 kHz of the resonance frequency.

It also shows that for given parameters L₁, L₂, n₁ and n₂ there existsan optimum load resistance R_(LDC,opt) that minimizes losses in powerconversion and in the resonant inductive link thus maximizing end-to-endefficiency. End-to-end efficiency may be defined as

$\begin{matrix}{\eta_{e\; 2e} = \frac{P_{LDC}}{P_{SDC}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where P_(LDC)=V_(LDC)·I_(LDC) and P_(SDC)=V_(SDC)·I_(SDC) denote the DCload (output) power and the DC source (input) power. Conversely, givenload resistance and transformation ratios n₁ and n₂, there exists anoptimum pair of inductance L_(1,opt) and L_(2,opt) or alternatively,given L₁ and L₂, an optimum pair of ratio n_(1,opt) and n_(2,opt)maximizing efficiency η_(e2e).

In the following for the sake of efficiency of the mathematicalequations but without loss of generality, it is assumed that thewireless power system is fully symmetric, meaning that

V _(DC) =V _(SDC) =V _(LDC)  Equation 4

n=n ₁ =n ₂  Equation 5

L=L ₁ =L ₂  Equation 6

R _(eq) =R _(eq,1) =R _(eq,2)  Equation 7

It can be shown that conclusions drawn from this specific case can alsobe applied to the general case of an asymmetric system.

Furthermore, it is assumed that both CB and BEV power conversion arelossless and that instead power conversion losses are accounted for inthe equivalent loss resistances R_(eq,1) and R_(eq,2), respectively.Evidently, the efficiency of the resonant inductive link that can bedefined as the ratio of output power-to-input power

$\begin{matrix}{\eta = \frac{P_{2}}{P_{1}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

equals to the end-to-end efficiency η_(e2e) as defined above.

Assuming switched-mode power conversion with a 50% duty cycle, voltageV₁ and V₂ are both square waves. Though filtered by the effect ofresonance, antenna currents I₁ and I₂ are generally non-sinusoidal withharmonics content depending on coupling coefficient. Thus some power istransmitted via harmonics. In most cases however, energy transfer viaharmonics is negligible. For the purpose of illustration, currents areassumed substantially sinusoidal such that CB antenna input power andBEV antenna output power can be defined as

$\begin{matrix}{P_{1} \cong \frac{V_{1,0}}{I_{1,0}}} & {{Equation}\mspace{14mu} 9} \\{P_{2} \cong \frac{V_{2,0}}{I_{2,0}}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

with voltages and currents referring to the r.m.s. of the fundamentalcomponent at LF. For system dimensioning, it can be shown that thereexist basically two equations.

The first equation yields an optimum antenna coil inductance

$\begin{matrix}{L_{opt} \cong \frac{R_{L,0}}{\omega_{0}{k(d)}}} & {{Equation}\mspace{14mu} 11}\end{matrix}$

maximizing η, given coupling coefficient k(d), and angular operatingfrequency ω₀, and load resistance

$\begin{matrix}{R_{L,0} = \frac{V_{2,0}}{I_{2,0}}} & {{Equation}\mspace{14mu} 12}\end{matrix}$

as presented by BEV power conversion at fundamental frequency.

The mathematical derivation of Equation 11 is further describedhereinbelow. Equation 11 is valid in a strongly coupled regime whereL_(opt) is practically independent of the actual loss resistance R_(eq).However, it will depend on the load resistance and the couplingcoefficient, which generally need to be adapted if load resistanceand/or separation of CB and BEV antenna are changed.

A second equation relates energy transfer rate P₂ and couplingcoefficient k(d) to the generated magnetic field

$\begin{matrix}{{H^{2}(r)} \cong {\frac{c( {g_{1},g_{2},r} )}{\omega_{0}}\frac{P_{2}}{k(d)}}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

Here c shall denote a factor that takes into account the CB and BEVantennas geometry g₁ and g₂, and the position the magnetic fieldstrength refers to, defined by the position vector r as illustrated inFIG. 17 and the mathematical derivation is further describedhereinbelow. Equation 13 assumes that position r is enough distant toantenna coils so that a change of their separation in the range ofinterest excerpts virtually no influence on the magnetic field atreference position, except the effect of their mutual coupling.

Introducing a regulatory constraint, e.g. magnetic field strengthH(r_(m)) measured at a position r_(m) in defined distance shall notexceed a defined limit H_(lim), provides a limit for the energy transferrate

$\begin{matrix}{P_{2,\max} \cong {\frac{\omega_{0}}{c( {g_{1},g_{2},r_{m}} )}{k(d)}H_{\lim}^{2}}} & {{Equation}\mspace{14mu} 14}\end{matrix}$

Equation 14 demonstrates that maximum energy transfer rate decreasesproportionally to the coupling coefficient. For example, assuming amaximum power of 4 kW at a coupling coefficient of 0.4, power is limitedto 2 kW if antenna separation is increased so that a couplingcoefficient of 0.2 results.

Now using the definitions of the voltage and current transformationratio as applicable to the fundamental component

n ₀:1=V _(2,0) :V _(LDC) =I _(DCL) :I _(2,0),  Equation 15

the corresponding load resistance

$\begin{matrix}{{R_{L,0} = {\frac{n_{0}V_{LDC}}{( \frac{1}{n_{0}} )I_{LDC}} = {{n_{0}^{2}R_{LDC}} = {n_{0}^{2}\frac{V_{LDC}^{2}}{P_{LDC}}}}}},} & {{Equation}\mspace{14mu} 16}\end{matrix}$

in terms of DC load voltage V_(LDC) and DC load power P_(LDC), and theassumption of a lossless power conversion P₂=P_(LDC) Equation 11 may bewritten

$\begin{matrix}{{L_{opt} \cong \frac{R_{L,0}}{\omega_{0}{k(d)}}} = {\frac{n_{0}^{2}R_{LDC}}{\omega_{0}{k(d)}} = \frac{n_{0}^{2}V_{LDC}^{2}}{\omega_{0}{k(d)}P_{2}}}} & {{Equation}\mspace{14mu} 17}\end{matrix}$

Substituting P₂ by Equation 14 provides a relation between L_(opt),k(d), and n₀

$\begin{matrix}{L_{opt} \cong {\frac{c( {g_{1},g_{2},r_{m}} )}{\omega_{0}} \cdot \frac{n_{0}^{2}}{k^{2}(d)} \cdot \frac{V_{LDC}^{2}}{H_{\lim}^{2}( r_{m} )}}} & {{Equation}\mspace{14mu} 18}\end{matrix}$

To satisfy Equation 18 that ensures maximum efficiency and regulatorycompliance, either antenna inductance L=L₁=L₂, or transformation ration=n₁=n₂, or both have to be adapted when distance is changed. If everpossible, varying antenna inductance should be avoided as in general itwill involve complex switching circuitry or mechanical gear, additionallosses and non-optimum use of antenna volume thus loss of qualityfactor. It also requires variable capacitance to maintain resonance,thus adding to complexity. The use of an additional antenna matchingnetwork acting as a transformer may bring along similar drawbacks.

A less complex and more economical solution may be achieved by usingpower conversion to provide the required variable transformation ratio.Changing CB-side transformation ratio n₁ is equivalent to power controlsince it will largely affect energy transfer rate across the link.Changing BEV-side transformation ratio n₂ accordingly will ensure thatthe wireless power link is operated efficiently. it may be called loadadaptation.

Several methods for power control and load adaptation have been proposedwith some allowing for continuous change of transformation ratio,however sacrificing zero current switching (ZCS), thus leades to someincreased switching loss and stress of switching devices. Others methodsmay maintain ZCS condition, but permit change of transformation ratioonly in coarse steps.

One method to change transformation ratio and that is extremelylow-loss, is to change the operational mode of the bridge (e.g., fromfull-bridge mode to half-bridge mode or vice versa). This method isfurther described hereinbelow.

The basic circuit diagram of a full-bridge-based series resonantwireless energy transfer system is displayed in FIG. 18. CB-sideswitches S_(1j) may represent FET or IGBT solid state devices, whilstswitches of BEV-side LF-to-DC power conversion may be passive diodes butalso active devices, in case of synchronous rectification.

In full or H-bridge mode, all switches of power conversion are togglingin a manner that S_(j1) and S_(j2′) are closed at the same time. WhenS_(j1) is closed then S_(j2) and S_(j1′) are open and vice versa. Thisapplies to CB-side and BEV-side power conversion (j∈{1,2}).

In half-bridge mode e.g. only S₁₁ and S_(11′) are toggling and S_(12′)and S₁₂ are static. When S₁₁ is closed then S_(11′) is open and viceversa. In the static half-bridge e.g. S_(12′) may be closed. The factthat current needs to pass switch S_(12′) causes some extra losses,which would not exist in a non-adaptive half-bridge-based system.However this additional CB-side and BEV-side switch on-state resistanceis considered a low price for a system that is capable efficientadaptation to two different transfer distances.

In case of a unidirectional energy transfer system using a passive diodefull-bridge rectifier in BEV-side power conversion, one half-bridgeneeds to be supplemented with active switches (FETs or IGBTs) inparallel to the diodes. These transistors however need only be staticswitches.

It can be shown that a full-bridge transforms a DC voltage level into aLF voltage level of the fundamental by

$\begin{matrix}{n_{0} = \frac{\sqrt{8}}{\pi}} & {{Equation}\mspace{14mu} 19}\end{matrix}$

which is approximately 1.Correspondingly, a half-bridge transforms by

$\begin{matrix}{n_{0} = \frac{\sqrt{2}}{\pi}} & {{Equation}\mspace{14mu} 20}\end{matrix}$

which is approximately ½.

Now a system that is capable to adjust BEV antenna to two discretez-positions corresponding to a shorter distances d′ and a longerdistance d″, respectively, is considered. If conditions permit, thesystem uses the shorter distance e.g. that corresponds to a couplingcoefficient k(d′), else it adjusts to d″ corresponding to k(d″).Distances are chosen such that

k(d′)=2·k(d″)  Equation 21

From Equation 18, Equation 19, Equation 20, and Equation 21, it becomesevident that an inductance L_(opt) can be found that is optimum at bothdistances, if the system operates in full-bridge mode at distance d′ andin half-bridge mode at distance d″. This is proved by defining

$\begin{matrix}{c^{\prime} = {\frac{c( {g_{1},g_{2},r_{m}} )}{\omega_{0}} \cdot \frac{V_{LDC}^{2}}{H_{\lim}^{2}( r_{m} )}}} & {{Equation}\mspace{14mu} 22}\end{matrix}$

and by expressing the optimum antenna inductance (Equation 18) asfollows:

$\begin{matrix}{\begin{matrix}{L_{opt} \cong {c^{\prime} \cdot \frac{8}{\pi^{2}{k^{2}( d^{\prime} )}}}} \\{= {c^{\prime} \cdot \frac{2}{\pi^{2}{k^{2}( d^{''} )}}}} \\{= {c^{\prime} \cdot \frac{2}{\pi^{2}{{k^{2}( d^{\prime} )}/4}}}}\end{matrix}\quad} & {{Equation}\mspace{14mu} 23}\end{matrix}$

An example of a system that is capable to optimally adapt to twodifferent distances by changing mode of power conversion whileattempting to maintain maximum efficiency and maximum power withinregulatory constraints is shown in the table below.

TABLE 1 Example of a system that optimally adapts to two differentdistances Distance Coupling Operating Transformation Energy transfer dcoefficient k(d) mode ratio n₀ rate P₂ [kW] 4.8 cm 0.4 Full-bridge$\frac{\sqrt{8}}{\pi}$ 4  10 cm 0.2 Half-bridge $\frac{\sqrt{2}}{\pi}$ 2Of course, this method of bridge reconfiguration may be combined withother methods of power control/load adaptation in order to adapt thelink to any distance within a predefined range and/or to throttle loadpower (battery charge current). Examples of alternative methods include(1) operating the link off-resonance by changing frequency, (2)intentional detuning of antennas, (3) using PWM drive waveforms withduty cycle <50%; (4) DC-to-DC converter in CB and BEV power conversion,(5) phase switching in case of 2-phase or 3-phase supply, etc. Thesemethods may all be considered directly or indirectly changingtransformation ratios n₁ and n₂.

In a practical system, transformation ratio and antenna z-axis positionwill be controlled by a control system (described above) with entitiesin the CB and BEV subsystem. These entities may communicate usingin-band or out-of-band signaling.

Regarding the derivation of Equation 11, the optimum load resistance ofa magnetically coupled resonant system may be derived by

R _(L,opt) =R ₂√{square root over (1+k ² Q ₁ Q ₂)}  Equation 24

where R₂ denotes the loss resistance of the resonant receive antenna, Q₁and Q₂ the Q-factors of the resonant transmit and receive antenna,respectively, and k the coupling coefficient. Loading the magnetic linkwith R_(L,opt) maximizes transfer efficiency.

In a strongly coupled regime

k ² Q ₁ Q ₂>>1  Equation 25

or in the so-called ‘magic’ regime where link efficiency is close to100%, Equation 24 may be simplified to

R _(L,opt) ≈R ₂√{square root over (k ² Q ₁ Q ₂)}  Equation 26

In a high power wireless energy transfer system, the assumption of astrongly coupled regime or even a ‘magic’ regime will be mostly valid.

Now assuming a fully symmetric link with

L=L ₁ =L ₂  Equation 27

R=R ₁ =R ₂  Equation 28

and substituting Q-factors Q₁ and Q₂ in Equation 26 by

$\begin{matrix}{Q = {Q_{1} = {Q_{2} = \frac{\omega_{0}L}{R}}}} & {{Equation}\mspace{14mu} 29}\end{matrix}$

yields

R _(L,opt) ≈kω ₀ L  Equation 30

Conversely, given the load resistance R_(L), there exists an optimumantenna inductance

$\begin{matrix}{L_{opt} \cong \frac{R_{L}}{k\; \omega_{0}}} & {{Equation}\mspace{14mu} 31}\end{matrix}$

that maximizes efficiency.

Regarding the derivation of Equation 13, the magnetic field strength asproduced at a location r by the BEV antenna that is in essence amulti-turn wire loop may be expressed as

H ₂(r)=N ₂ ·I _(2,0)·γ(g ₂ ,r)  Equation 32

where N₂ denotes number of turns of the antenna coil, I_(2,0) theantenna current at fundamental, and γ is basically a function of itsgeometry g₂ and position vector r where the field strength refers to.Equation 32 assumes that varying the number of turns would not changethe antenna coils geometry, hence g₂≠ƒ(N₂).

The inductance of the multi-turn loop may be expressed as

L ₂ =N ₂ ²·β(g ₂)  Equation 33

where β is basically a function of coil geometry g₂.

The load resistance may be expressed as a function of power P₂ andcurrent I_(2,0) as follows:

$\begin{matrix}{R_{L,0} \cong \frac{P_{2}}{I_{2,0}^{2}}} & {{Equation}\mspace{14mu} 34}\end{matrix}$

Now using Equation 11 and substituting above equations yields

$\begin{matrix}{{N_{2}^{2} \cdot {\beta ( g_{2} )}} \cong \frac{P_{2}}{\omega_{0}{{k(d)} \cdot I_{2,0}^{2}}}} & {{Equation}\mspace{14mu} 35}\end{matrix}$

and with some manipulations also using Equation 32, we obtain for thesquare of the magnetic field strength at position r

$\begin{matrix}{{N_{2}^{2} \cdot I_{2,0}^{2} \cdot {\beta ( g_{2} )}} = {{{H_{2}^{2}(r)}\frac{\beta ( g_{2} )}{\gamma^{2}( {g_{2},r} )}} \cong {\frac{P_{2}}{\omega_{0}{k(d)}}.}}} & {{Equation}\mspace{14mu} 36}\end{matrix}$

Defining

$\begin{matrix}{{c( {g,r} )} = \frac{\gamma^{2}( {g_{2},r} )}{\beta ( g_{2} )}} & {{Equation}\mspace{14mu} 37}\end{matrix}$

yields

$\begin{matrix}{{H_{2}^{2}(r)} \cong {\frac{c( {g_{2},r} )}{\omega_{0}}\frac{P_{2}}{k(d)}}} & {{Equation}\mspace{14mu} 38}\end{matrix}$

So far CB antennas contribution to the magnetic field which is accordingto Equation 32

H ₁(r)=N ₁ ·I _(1,0)·γ(g ₁ ,r)  Equation 39

has been neglected.

In the symmetric case, number of turns N₁ equals N₂ and current I_(1,0)of CB antenna will change proportionally to I_(2,0). Hence contributionsfrom CB and BEV antenna H₁(r) and H₂(r) at location r will also changeproportionally, because

$\begin{matrix}{\frac{P_{2}}{P_{1}} = {\frac{V_{2,0}I_{2,0}}{V_{1,0}I_{1,0}} = {\frac{I_{2,0}}{I_{1,0}} = \eta}}} & {{Equation}\mspace{14mu} 40}\end{matrix}$

given that V_(SDC)=V_(LDC) hence V_(1,0)=V_(2,0).

It can be easily shown that proportions would also remain in theasymmetric case (N₁≠N₂) if N₂ was changed in a process of optimization.Defining c(g₁,g₂,r) that takes into account geometry of both antennas aswell as the phase offset of I_(1,0) relative to I_(2,0), which in caseof resonance is always 90 degrees independent of the mutual coupling,the sum field may be expressed as

$\begin{matrix}{{{H^{2}(r)} \cong {\frac{c( {g_{1},g_{2},r} )}{\omega_{0}}\frac{P_{2}}{k(d)}}},} & {{Equation}\mspace{14mu} 41}\end{matrix}$

which is Equation 13.

FIGS. 19A and 19B illustrate two circuit configurations of an adaptableseries resonant energy transfer system, in accordance with an exemplaryembodiment. In FIG. 19A, configuration A assumes (1) a longer distanceor in general a looser coupling between transmit and receive antenna,(2) both transmit and receive side power conversion operate inhalf-bridge mode. In FIG. 19B, configuration B assumes (1) a shorterdistance or in general a tighter coupling between transmit and receiveantenna, (2) both transmit and receive side power conversion operate infull-bridge mode.

Both configurations assume a constant voltage source and a constantvoltage sink. This assumption is useful but also very reasonableconsidering a system that transfers energy from the power grid to avehicles battery (G2V) or vice versa (V2G). This analysis of thewireless power link reveals:

1) Energy transfer rate (power P) doubles with configuration B withoutthe need for adapting

-   -   Supply voltage and sink voltage    -   Reactance of resonant antennas (inductances and capacitances)        both implemented without additional circuitry and/or mechanics        for power/voltage conversion and/or variable reactance.        2) Both configurations are optimally matched to achieve maximum        energy transfer efficiency.        3) Both configurations are equivalent in terms of magnetic field        strength as measured in the antennas vicinity, thus potential to        fully exploiting a regulatory/EMC constraint.

A constant voltage sink (battery) is assumed as opposed to a constantload resistance. Summarizing, an adaptive system and a method totransfer energy from a voltage source to a voltage sink either over alonger distance (looser coupling) with a lower power or over a shorterdistance (tighter coupling) with a higher power is disclosed, where thesystem is adaptable to operate at maximum efficiency, also optimallyexploiting a regulatory limit, solely by changing mode of operation oftransmit and receive side power conversion to either half-bridge mode orfull-bridge mode, respectively.

FIG. 20 illustrates wireless power transfer components for a wirelesspower transfer system, in accordance with an exemplary embodiment of thepresent invention. Regarding sensing, communication and control, awireless power system that adapts to the actual conditions while aimingat a maximum performance and efficiency of the wireless power link makesuse of ancillary functions for sensing, communication, and control.These ancillary functions may be part of the BEV wireless chargingsystem 2000 whose generic architecture is displayed in FIG. 20.

The system 2000 can be subdivided into two major subsystems: theCharging Base subsystem (CB-SS) 2002 and the Battery Electric Vehiclesubsystem (BEV-SS) 2004. The CB subsystem 2002 is comprised of

-   -   (1) CB power conversion (CB-PCONV) 2006 that converts DC power        or AC power at supply frequency into transmit power at operating        frequency (e.g. LF) or vice versa in reverse mode of operation        (V2G). it integrates several sensors to measure voltages and        currents as shown in a simplified circuit diagram of FIG. 21.    -   (2) CB antenna module (CB-ANT) 2008 that contains CB antenna        coil and that can transmit or receive ‘wireless’ power to/from        the BEV antenna 2010. CB antenna coil is assumed fixed and        ground-embedded.    -   (3) CB communication transceiver (CB-COM) 2012 that communicates        with the BEV to exchange system control data but also data to        identify or authenticate the BEV or data that is generated by        other applications directly or indirectly related to BEV        charging. CB-COM 2012 may use a dedicated antenna or may make        reuse of CB-ANT 2008.    -   (4) CB control unit (CB-CTRL) 2014 that processes data received        from the BEV and the various sensors of the CB subsystem 2002        and controls the different entities of the CB subsystem 2002.

The BEV subsystem 2004 is comprised of

-   -   (1) BEV power conversion (BEV-PCONV) 2016 that converts        ‘wireless’ power received at operating frequency (e.g. LF) into        DC power or AC power at supply frequency or vice versa in        reverse mode of operation (V2G). BEV-PCONV integrates several        sensors to measure voltages and currents as shown in FIG. 21.    -   (2) BEV antenna module (BEV-ANT) 2010 that contains the BEV        antenna coil and that can receive or transmit ‘wireless’ power        from/to the BEV antenna 2010. BEV antenna coil is assumed        movable in X, Y, Z-direction. BEV-ANT 2010 also integrates at        least one sensor (S) to detect unwanted objects like stones,        debris, snow, ice, etc. that may constrain degree of freedom of        BEV antenna e.g. to move to a low enough z-position. Sensors may        include at least one of a mechanical resistance sensor        integrated in antennas mechanics, a tactile sensor at antenna        modules surface, an ultrasonic sensor, an optical sensor, and an        electromagnetic sensor to detect metallic objects.    -   (3) BEV-ALIGN 2018 that encompasses all the functionality to        properly align the BEV antenna coil to the CB antenna coil and        to adjust distance for a desired coupling. This entity includes        an actuator that may be a servo-motor (M) driving BEV antenna        mechanics. BEV-ALIGN 2018 may also integrate sensors to detect        mechanical resistance.    -   (4) BEV communication transceiver (BEV-COM) 2020 that        communicates with the CB to exchange system control data but        also data to identify or authenticate the BEV or data that is        generated by other application directly or indirectly related to        BEV charging. BEV-COM 2020 may use a dedicated antenna or may        make reuse of BEV-ANT 2010.    -   (5) BEV control unit (BEV-CTRL) 2022 that processes data        received from the CB and the various sensors of the BEV        subsystem 2004 and controls the different entities of the BEV        subsystem 2004.

In the following, a procedure is described how this system may adapt tolocal conditions to maximize energy transfer rate and efficiency.

Transmit power may have to be reduced while the system adjusts to a newdistance/coupling coefficient. There exist several methods of transmitpower control that may apply to throttle power for link adjustmentpurposes. Since power can be significantly reduced, efficiency is lessof an issue in this mode of operation.

If conditions permit and higher power (e.g. 4 kW) is desired, the systemadjusts to a defined coupling k′ at distance d′. Else, if conditions donot permit because objects on ground are detected by at least one ofsensors (S) or if lower power (e.g. 2 kW) is desired, the system adjuststo a weaker but defined coupling k″=k/2 at larger distance d″.

Since the relationship between coupling coefficient and distance maydiffer to some degree, depending on local conditions, it may bedesirable to measure coupling coefficient k(d) rather than relying ondistance.

BEV-CTRL can determine coupling coefficient k(d) by using measurementdata from voltage and current sensors of BEV power conversion and CBpower conversion that is transmitted from CB-CTRL to BEV-CTRL via thecommunication link. Knowing link parameters (L₁, C₁, R₁, L₂, C₂, R₂) andoperating frequency as well as parameters of power conversion, couplingcoefficient k(d) can be computed sufficiently accurate e.g. from thesystem of equations of the resonant inductive link

$\begin{matrix}{{{V_{1} - {R_{1}I_{1}} - {{j( {{\omega \; L_{1}} - \frac{1}{\omega \; C_{1}}} )}I_{1}} - {{j\omega}\; {MI}_{2}}} = 0}{{V_{2} - {R_{1}I_{2}} - {{j( {{\omega \; L_{2}} - \frac{1}{\omega \; C_{2}}} )}I_{2}} - {{j\omega}\; {MI}_{2}}} = 0}} & {{Equation}\mspace{14mu} 42}\end{matrix}$

Once BEV antenna is properly adjusted to one of the two target couplingcoefficients (k′ or k″), CB-PCONV and BEV-PCONV are configured tofull-bridge mode (in case of k′) or half-bridge mode (in case of k″) andpower is ramped up to maximum power that is permissible at this targetcoupling coefficients (e.g. 4 kW or 2 kW, respectively).

A more generic approach to adapting the system to any couplingcoefficient may define a threshold for the coupling coefficient. Ifmeasured coupling coefficient is above that threshold, power conversionis configured to full-bridge mode. Conversely, if coupling coefficientis equal or below that threshold, power conversion is configured tohalf-bridge mode. This threshold may be defined somewhere halfwaybetween the two target coupling coefficients e.g. at a value where bothfull-bridge mode and half-bridge mode would perform equally well (e.g.equal efficiency). However, operating the system at a couplingcoefficient considerably deviating from the two target couplingcoefficients may require additional means to control power, efficiency,and emission levels as described above.

Operation at defined coupling coefficients k′ and k″ in eitherfull-bridge or half-bridge mode, respectively, as the basic mode ofoperation provides optimum energy transfer at maximum efficiency withlowest complexity in power conversion. Fine control to precisely adjustpower to nominal power can be achieved by lowering or increasingcoupling slightly or by another method that does not noticeably degradeefficiency.

FIG. 22 is a flowchart of a method for adaptive power conversion, inaccordance with an exemplary embodiment of the present invention. Amethod 1800 includes a step 1802 for converting a power from a powersupply system to a power at an operating frequency for transfer ofwireless energy according to an adaptable power converter reconfigurableto operate between at least first and second modes. The method 1800further includes a step 1804 for generating at least one of an electricand magnetic field by a transmit antenna resonant near the operatingfrequency to transfer the wireless energy to a receive antennapositioned within a near field coupling-mode region, the near fieldcoupling-mode region configured to be accessible by the receive antenna.

Exemplary embodiments are directed to wireless power transfer usingmagnetic resonance in a coupling mode region between a charging base(CB) and a remote system such as a battery electric vehicle (BEV). Thewireless power transfer can occur from the CB to the remote system andfrom the remote system to the CB. Load adaptation and power controlmethods can be employed to adjust the amount of power transferred overthe wireless power link, while maintaining transfer efficiency.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the exemplary embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the exemplary embodiments of the invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the exemplary embodiments disclosed herein may beimplemented or performed with a general purpose processor, a DigitalSignal Processor (DSP), an Application Specific Integrated Circuit(ASIC), a Field Programmable Gate Array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theexemplary embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module may reside in Random AccessMemory (RAM), flash memory, Read Only Memory (ROM), ElectricallyProgrammable ROM (EPROM), Electrically Erasable Programmable ROM(EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any otherform of storage medium known in the art. An exemplary storage medium iscoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium may be integral to the processor. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosed exemplary embodiments isprovided to enable any person skilled in the art to make or use thepresent invention. Various modifications to these exemplary embodimentswill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other embodiments withoutdeparting from the spirit or scope of the invention. Thus, the presentinvention is not intended to be limited to the exemplary embodimentsshown herein but is to be accorded the widest scope consistent with theprinciples and novel features disclosed herein.

What is claimed is:
 1. An apparatus for wirelessly transmitting power,the apparatus comprising: a power conversion circuit configured toconvert power received from a power supply and operate in at least oneof a first mode and a second mode; a first power transfer componentelectrically coupled to the power conversion circuit, the first powertransfer component configured to wirelessly transfer charging power to asecond power transfer component at a receiver based at least in part onthe converted power; and a controller configured to reconfigure thepower conversion circuit between at least the first and second modesbased at least in part on a value indicative of a degree of couplingbetween the first and second power transfer components.
 2. The apparatusof claim 1, wherein the first mode corresponds to a full-bridge mode andthe second mode corresponds to a half-bridge mode.
 3. The apparatus ofclaim 2, wherein the controller is configured to reconfigure the powerconversion circuit to operate in the first mode in response to detectingthe indicative value is greater than a threshold.
 4. The apparatus ofclaim 2, wherein the controller is configured to reconfigure the powerconversion circuit to operate in the second mode in response todetecting the indicative value is less than a threshold.
 5. Theapparatus of claim 1, further comprising a switching circuit configuredto phase-switch the power conversion circuit when the power receivedfrom the power supply comprises 2 or more phases.
 6. The apparatus ofclaim 1, further comprising a pulse-width modulation circuitelectrically coupled to the power conversion circuit, the pulse-widthmodulation circuit configured to operate with a duty cycle of less than50%.
 7. The apparatus of claim 1, further comprising a sensor configuredto detect at least one object between the first and second powertransfer components, wherein the first power transfer component isconfigured to move in an x, or y, or z-direction based at least in parton the at least one detected object.
 8. The apparatus of claim 8,wherein the sensor comprises at least one of a mechanical resistancesensor, or a tactile sensor, or an ultrasonic sensor, or an opticalsensor, or an electromagnetic sensor, or any combination thereof.
 9. Theapparatus of claim 1, wherein the first power transfer component isfurther configured to move between two discrete z-positionscorresponding to a shorter distance and a longer distance between thefirst and second power transfer components, and wherein the powerconversion circuit is further configured to operate in the first modewhen the second power transfer component is located at the shorterdistance and the second mode when the second power transfer component isat the longer distance.
 10. The apparatus of claim 1, wherein thecontroller is configured to reconfigure the power conversion circuitbetween at least the first and second modes based at least in part on adistance between the first and second power transfer components.
 11. Theapparatus of claim 1, wherein the power conversion circuit is furtherconfigured to convert the received power to an alternating current at awireless power transfer operating frequency.
 12. The apparatus of claim1, further comprising a resonant circuit comprising the first powertransfer component, wherein the resonant circuit is configured to besubstantially resonant at an operating frequency.
 13. The apparatus ofclaim 12, wherein the controller is configured to at least one of causethe resonant circuit to operate off-resonance or partially detune theresonant circuit based at least in part on the value indicative of thedegree of coupling.
 14. A method of wirelessly transmitting power,comprising: converting power received from a power supply by a powerconversion circuit; operating the power conversion circuit in at leastone of a first mode and a second mode; wirelessly transferring chargingpower from a first power transfer component to a second power transfercomponent of a receiver based at least in part on the converted power;and reconfiguring the power conversion circuit between the first andsecond modes based at least in part on a value indicative of a degree ofcoupling between the first and second power transfer components.
 15. Themethod of claim 14, wherein the first mode corresponds to a full-bridgemode and the second mode corresponds to a half-bridge mode.
 16. Themethod of claim 15, wherein reconfiguring the power conversion circuitbetween the first and second modes comprises reconfiguring the powerconversion circuit to operate in the first mode when the indicativevalue is greater than a threshold.
 17. The method of claim 15, whereinreconfiguring the power conversion circuit between the first and secondmodes comprises reconfiguring the power conversion circuit to operate inthe first mode when the indicative value is less than a threshold. 18.The method of claim 14, further comprising: detecting at least oneobject between the first and second power transfer components; andmoving the first power transfer component in at least one of an x, or y,or z-direction based at least in part on the at least one detectedobject to increase coupling between the first and second power transfercomponents.
 19. An apparatus for wirelessly transmitting power, theapparatus comprising: means for converting power received from a powersupply; means for operating the converting means in at least one of afirst mode and a second mode; means for wirelessly transferring chargingpower to a power transfer component based at least in part on theconverted power; and means for reconfiguring the converting meansbetween the first and second modes based at least in part on a valueindicative of a degree of coupling between the transferring means andthe power transfer component.
 20. An apparatus for wirelessly receivingpower at an electric vehicle, the apparatus comprising: a first powertransfer component configured to wirelessly receive charging power via amagnetic field generated by a second power transfer component of atransmitter and provide the charging power to a load of the electricvehicle; a sensor configured to detect at least one object between thefirst and second power transfer components; and a controller configuredto cause the first power transfer component to move in at least one ofan x, or y, or z-direction based on at least one of the at least onedetected object or a value indicative of a degree of coupling betweenthe power transfer components.